GB411741A - Process for the conversion of unsaturated alcohols - Google Patents

Abstract

Unsaturated alcohols, which may be further substituted by halogen, alkyl, alkoxy, aryl, aryloxy, aralkyl or aralkoxy radicles, are converted into their saturated isomeric aldehydes or ketones by heating, preferably under pressure, a substantially homogeneous liquid system comprising the alcohol to be converted and an acid catalyst, e.g. a mineral acid such as sulphuric acid or an acid salt thereof. As the reaction proceeds, the solution becomes saturated with isomer and its separation out as a second phase is avoided. In the case of compounds which are readily volatile under the conditions of the reaction, any aldehyde or ketone tending to appear as a second phase is evaporated by keeping the pressure in the reaction vessel below the vapour pressure of the isomer at the reaction temperature. The isomer thus evaporated is recovered by condensation and any unreacted alcohol and water are separated by fractional distillation. The fractionating apparatus is preferably adjacent to the reaction vessel, isomer or isomer and water being fed to the top of the column as reflux, aqueous isomer being recovered as distillate, and may be further dehydrated by salting and/or re-distillation. To avoid salting, the distillate from the fractionating column may be cooled, and the isomer layer may be returned to the column as reflux and the aqueous layer to the reaction vessel. When the distillate becomes homogeneous, it is collected as an intermediate cut until the anhydrous isomer distils over. The intermediate cut may be added to the reaction vessel. In continuous operation, the concentration of alcohol in the reaction vessel is maintained by feeding alcohol at the rate at which it is re-arranged or removed by distillation. The alcohol is preferably introduced near the bottom of the reaction liquid by means of a perforated disc or porous tube, and may be the residue from the fractionating apparatus. Alternatively, the decreased solubility of alcohol and isomer at lower temperatures is utilised. When the reaction has progressed to the point at which the isomer in the liquid phase has reached saturation, the liquid is removed from the reaction vessel and cooled. The isomer collects as a separate layer or may be extracted by solvents, e.g. when treating a polyhydroxy-olefine, the resulting product may be soluble in water. Unchanged alcohol is returned to the reaction vessel after the isomer has been purified. The optimum reaction temperature is usually above the boiling point of the reaction mixture, and increased pressure must then be applied. The olefine alcohol may contain varying amounts of water, e.g., its constant boiling mixture with water may be used. Suitable catalysts include phosphoric acid, sulphuric acid, hydrochloric acid, perchloric acid, benzene sulphonic acid and its homologues, acid salts of the polybasic acids, and acid alkyl esters. The preferred catalyst is aqueous sulphuric acid containing less than 20 per cent H<2>SO4, preferably between 10 per cent and 15 per cent. According to examples (1) Isobutenol is fed with agitation into a vessel containing a quantity of 10--13 per cent aqueous sulphuric acid heated to a temperature between 90--120 DEG C., preferably above 105 DEG C. The vapour is led to an intermediate section of a fractionating column and the product, isobutyraldehyde, is separated according to the method described above. The pressure in the reaction vessel is about 2 atmospheres. (2) The top layer of an azeotropic mixture of isobutenol and water was steadily passed into a leadlined kettle provided with a fractionating column and containing 13 per cent aqueous sulphuric acid. The temperature was maintained at 114 DEG C., and the pressure at 2 atmospheres. An azeotropic mixture of aldehyde and water was distilled over. (3) A mixture of the isomeric alcohols:--1 - phenyl - 2 - hydroxymethyl - 3 - chlorpropene : 1 - phenyl - 1 - chlor - 2 - hydroxymethyl - propene and 1 - phenyl - 1 - hydroxy - 2 - methyl - 3 - chlorpropene (obtained by hydrolysing the chlorination product of phenyl isobutene in an autoclave for 30 minutes at 120 DEG C., with 10 per cent aqueous caustic soda lye) was treated with 10 per cent sulphuric acid at 100 DEG C., for 45 minutes with agitation. The mixture was extracted with ether and the product was a mixture of 2 - benzyl - 3 - chlorpropionaldehyde : 3 - phenyl - 3 - chlor - 2 - methyl - propionaldehyde and 1 - chlor - isopropyl - phenyl - ketone. (4) 15 per cent aqueous sulphuric acid was maintained at 95--100 DEG C. with rapid stirring in the apparatus described in examples (1) and (2) and 2 - methylbutene - 2 - ol - 4 (obtained by hydrolysis of a chlorinated arylene cut of cracked gasoline) was steadily fed to the bottom of the kettle. An azeotropic mixture of water and isovaleraldehyde distilled over at 85--90 DEG C., under atmospheric pressure. (5) In a similar manner, 2-methyl-butene-1-ol-3 was heated with 14 per cent sulphuric acid at 130 DEG C., and under 3,7 atmospheres pressure. Methyl-isopropylketone was obtained. (6). 1-chlor-2-methyl propene-1-ol-3 (obtained by hydrolysing chlorinated isocrotyl chloride) was slowly dripped into 15 per cent sulphuric acid at 100 DEG C. The reaction was stopped, and the heavy oily layer withdrawn. This procedure was repeated several times and the total volume of oily liquid was fractionated, and the contents of the flask were ether extracted. The products were b -chlor-isobutyraldehyde and a high boiling polymer. (7) 2-hydroxy-methyl-propene-1-ol-3 were heated with 13 per cent aqueous sulphuric acid. The mixture was ether extracted, several batches being so treated. The extract was fractionated, the main product being b -hydroxy-isobutyraldehyde and a small amount of polymer as residue.